Upgrading tube for a MAC 275 mk5 what are you using?

I have a MAC 275 mk5 new this year and I'm looking to re-tube it as i don't like the factory tubes. I find they are too bright and lack midrange tone. I'm using Spendor D9.2's that are rather unforgiving on the top end, supper detailed but lack some midrange tone as well when driven with the current tubes.

What tubes are others using, NOS? new production? KT88's or 6550. I'm personally leaning towards the 6550's.

What about the driver tubes? I've never owned an amp that used the 7AT's what are people recommending for them? 

I drive the 275 in balanced mode with my Mac C2700 preamp. 

thanks for your experiences 


Most of the Mac people I have spoken with prefer the KT88 Gold Lion tubes.  The consensus is that they make the amp sound its best.  I haven't heard the amp in that configuration, but I did not care for the Gold Lions in my C2500 tube preamp.  I like the McIntosh branded tubes (JJ) better in the pre.

I'm personally thinking NOS tubes, I've tried the gold lions in other tube types (300b,12 series small signal tubes, kt66, etc) and yes, they can be good.

I'm really wondering what NOS tubes people have tried, I've not used 12AT7 before so i'm not really sure which are great specially for the money ( i'm not paying $300 each for telies for example). I still want over all good sound from top to bottom but i'm looking for more midrange tone and sound stage depth and width. I find the JJ's if that's what Mcintosh is still using to be lacking in midrange tone and sound stage they are quiet, decent bass and decent up top if not a bit bright. But not like many of the NOS tubes I own. 

Also, anyone using 6550's opposed to the KT 88's? I find the KT series to be overall leaner in the midrange compared to other NOS types. 

RCA black plate 12at7 and 6201 offer a harmonically richer sound (I use 12at7 to drive 2A3's).

Mullard Blackburn production is also good for such.

Avoid Sylvania and Eastern European 12at7's as they are leaner/brighter (I also include Mullard box plate CV4024/12at7's from the Mitcham factory in this group).

For input/gain "12ax7's" (which your amp uses) I seem to always end up preferring Amperex Holland (the less expensive 60's short plates are still reasonably priced and their sound quality is up there with the older Holy Grail versions).

Google "Brent Jessee" to view his current inventory/pricing and specifically check out his damaged and rebranded label offerings if you do not require pretty tubes.






thanks for that information that’s very helpful. the tube store has some RCA’s on sale right now i may pick up a set to try out.

I actually have a few Amperex 12ax7’s in my house i may try in the amp/preamp. I agree i like these tubes as well.

also, my amps are Mk6 current production not the mk5. mistake sorry not that it makes much difference. 

thanks for the suggestions.




You just saved a bunch having the Amperex on hand.

The RCA 12at7's @ The Tube Store look good.

The tubes I did not recommend  are good tubes, just not for the type of sound you mentioned.

I have really fat sounding Ken-Rad dual flat plate 2A3's that I use Eastern Euro 12at7's with (balances out the sound), but stick with RCA/Mullard when running lighter sounding RCA and Visseaux 2A3's.

Most of my Amperex 12ax7's went into a friends Marantz 7 (wish I had more).




Interesting about the Ken-rads I also have a set of triode labs 2A3 mono blocks I really like a set of NOS RCA grey plates I found. They are one of my fav NOS tubes right now for 2a3, supposedly the black plates are even better but I've not heard them. The greys are rather balanced sounding with very good bass control and detail. not rolled off on top and of course supper midrange. much better than any new production tubes I've tried. 

I find the RCA dual GP a "tiny bit" warmer in the midrange than the BP (my system), but like both equally.

I did prefer one slightly over the other when I tried Fostex bullet tweeters with my Stephens-Trusonic 8" single drivers, but forget which.

The 12at7’s I use to drive the Ken-Rad 2A3’s are RFT (Germany).

They make the RCA’s sound thin, but compliment the Ken-Rads.

An odd thing about the Ken-Rads is that they test in the low 80’s (same on two TV-7D/U testers) and I’ve never had an RCA surpass 66 (usually low-mid 60’s) for NIB).

I’ve spent 3 of the Visseaux 2A3’s (out of 6) and benched the last pair, plus a spare, for if I ever get a soft start circuit/rectifer amp.